Field of the Invention
The present invention relates to a sheet storage apparatus for storing sheets, and an image forming apparatus including the sheet storage apparatus.
Description of the Related Art
Recently, image forming apparatuses, such as copiers, printers and facsimile machines, having a sheet feeding apparatus are widely used. Such an image forming apparatus feed a sheet with the sheet feeding apparatus to an image forming portion where an image is formed on the sheet. A typical sheet feeding apparatus includes a sheet feed cassette (sheet storage apparatus) that is drawably attached to the apparatus body and stores sheets to be fed to the image forming portion automatically. Some sheet feed cassettes include a sheet stacking portion on which sheets are stacked, and which is arranged to be lifted so that the sheets stacked thereon comes into contact with a sheet feed roller.
The sheet feed cassette having the sheet stacking portion includes a rear end regulation member. The rear end regulation member regulates a position of an upstream end (hereinafter referred to as a rear end), in a sheet feed direction, of the sheet stacked on the sheet stacking portion so as to allow a variety of sheets different in size to be stored in the cassette. Further, the sheet feed cassette is provided with a pair of side end regulation members that regulate a side end position in a direction orthogonal to the sheet feed direction (hereinafter referred to as a width direction).
The pair of side end regulation members of the sheet feed cassette regulates both side ends of the sheets while the rear end regulation member regulates the rear end of the sheets, so that the sheets are always positioned at the predetermined position. Thereby, sheets can always be fed from the same position on the sheet feed cassette stored in the apparatus body, and a stable sheet feeding performance can be achieved.
Meanwhile, there are increasing demands for realizing a large amount of printing on small-sized sheets such as postcards and envelopes. Conventionally, the small-sized sheets such as postcards and envelopes had to be fed through a manual sheet feed portion. Unfortunately, since the amount of sheets that can be stacked in the manual sheet feed portion was restricted to approximately 10 mm height, it was not suitable to perform printing on a large amount of sheets. In order to improve capability of massive printing, a sheet feed cassette allowing small-sized sheets to be stacked on is desirable, so that a large amount of the small-sized sheets are fed from the cassette. But generally, the minimum sheet size (A5 size, for example) that can be regulated using side end regulation members and rear end regulation member is larger than the small-sized sheets. Therefore, this kind of sheet feed cassette could not appropriately regulate the ends of the small-sized sheets smaller than the normally-used minimum sheet size (such as postcards and envelopes) with the side end regulation members and the rear end regulation member.
Here, Japanese Patent Application Laid-Open Publication No. 11-59925 discloses a sheet feed cassette having an auxiliary cassette (second cassette) capable of storing small-sized sheets and being attached to an inner side of a cassette body (first cassette). The second cassette includes a rear end regulation member and side end regulation members disposed at positions corresponding to ends of a sheet among small-sized sheets such as postcards and envelopes. This second cassette is attached to a sheet stacking portion of the first cassette, which is attached drawably to the apparatus body. This configuration enables the sheet feed cassette to regulate the ends of the small-sized sheet to be fed therefrom.
However, the side end regulation members and the rear end regulation member disclosed in the above document are fixed on the predetermined positions. Therefore, in order to feed multiple kinds of small-sized sheets different in size, it is necessary to prepare various types of second cassettes different in positions of side end regulation members and/or rear end regulation member positions. This configuration necessitates various types of second cassettes, which leads to increase in cost. Furthermore, users might feel inconvenient under this configuration because of time and labor required to select and replace the second cassettes manually each time the size of a small-size sheet in use is changed.